Composite alloy



United States Patent Ofiice 3,162,511 Patented Dec. 22, 1964 3,162,511 COMPOSITE ALLOY George S. Foerster and Milton I. Blubangh, Midland,

Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed July 18, 1963, Ser. No. 296,077 7 Claims. (Cl. 29-192) The invention relates to a composite, light weight metal body and method for making the same in which mag nesium is the major constituent. It more particularly concerns a die-expressed metallic body in which magnesium is the major constituent and which exhibits desirable strength characteristics at both ambient and elevated temperatures.

Composite solid metal alloy bodies having magnesium as the major constituent heretofore known which have been produced by die expressing particulate mixtures comprising magnesium have much to be desired as regards good room temperature properties despite possessing, in some instances, substantial resistance to creep at elevated temperatures. Accordingly, there is a desideratum in the art to provide composite solid magnesium alloy bodies having the light weight characteristic of magnesium which possess a combination of good strength properties both at room or ambient temperatures and at elevated temperatures such as are encountered in space craft operations and others where elevated temperatures prevail.

Thus, it is an object of the present invention to provide a magnesium-base alloy which has both good room temperature and high temperature properties and a method for making the same.

It is a further object of this invention to provide a magnesium-base alloy which has unusually high creep resistance and a method for making the same.

Other objects and advantages will appear as the description of the invention proceeds.

The term magnesium-base alloy, used herein, means a magnesium alloy containing at least 80 percent of magnesium by weight.

The term misch metal, used herein, means a rare earth alloy containing a major portion of cerium and minor portions of lanthanum, neodymium, praseodymium, Samarium, other rare earth elements plus traces of calcium, carbon, aluminum, silicon and iron.

The term didymium, used herein, means a rare earth alloy containing a major portion of neodymium, a minor portion of praseodymium plus other rare earth and other metals.

The invention is predicated upon the discovery that by subjecting to the extruding action of a conventional extrusion apparatus a mixture of certain metals comprising certain magnesium-base alloys and other metals, all in particulate form, whereby a solid alloy extrusion is obtained, the extrusion exhibits a desirable conformation of properties of both high temperature creep resistance and high strength at room temperature together with the lightness characteristic of magnesium alloys. The magnesium-base alloys with which the invention may be practiced are those containing the magnesium-soluble elements calcium (Ca), thorium (Th), cerium (Ce), lanthanum (La), praseodymium (Pr), misch metal and didymium. The magnesium alloy in particulate form is admixed with at least one of the metals antimony, silicon which is essentially insoluble in magnesium or aluminum (in the case where thorium is alloyed with magnesium), or an alloy thereof with magnesium, also in particulate form, these metals being capable of forming with magnesium binary metallic compounds. The resulting mixture is placed in the container of a conventional extrusion apparatus, heated and die expressed or extruded as in the conventional extrusion practice used with ordinary magnesiumbase alloys.

A microscopic examination of an etched specimen of a composite alloy produced by the method of the instant invention showed a grain boundary which appeared much more prominently as compared to the grain boundaries observed in a microscopic examination of each constituent of the composite alloy. It is believed that the silicon, antimony or aluminum (in the case where thorium is alloyed with magnesium) diffuses very slowly into the magnesium-base alloy grains but is able to move rather rapidly along the grain boundaries. There, it apparently reacts with thorium, calcium or a combination of some of the rare earth elements to form insoluble compounds which are more insoluble than the precipitated particles of the base alloy alone and are less prone to overaging. Therefore, the insoluble compound thus formed is much more efiiective than said precipitated particles in preventing grain boundary deformation, a primary mechanism for creep at elevated temperatures.

In carrying out the invention, magnesium alloyed with one of the magnesium-soluble metals aforesaid, viz., Ca, Th, Ce, La, Pr, misch metal and didymium, in conventional manner, is used in finely divided form. The proportions to employ are, in general, those normally present in the conventional binary magnesium alloy compositions. In the case of thorium, for example, it may be alloyed with the magnesium in an amount from about 0.05 to 6 percent by weight. It is preferable to use about 3 percent of thorium. The other alloying metals aforementioned may be used in similar amounts.

The aluminum, silicon, antimony or suitable metal containing one or more of these elements is also provided in finely divided form. These elements may be comminuted in any suitable way and mixed with the powdered magnesium-base alloy prior to die expression. The pro portions to be extruded with the magnesium-base alloy are about 0.05 to 3 percent. It is preferable to use about 1 percent silicon.

The metals, in the particulate form as aforesaid, are mixed together to form a uniform mixture of the metal particles. The mixture is charged into the heated container of a ram extruder having a suitable container and die opening and subjected to extrusion pressure to cause the heated metal mixture to be compacted and expressed through the die opening. One effect of the die expression operation is to produce coherence of each metal particle into a solid composite body.

The temperature of the metal mixture in the container may be the same as that conventionally employed for extruding the known magnesium-base alloys, e.g., from about 650 to 950 F. The ratio of the cross-sectional area of the extrusion container to that of the die opening has a material effect on the mechanical properties of the extrusion product. A desirable ratio is at least 10, although ratios as high as, or higher than, may be used.

The speed of extrusion may be varied over a wide range and depends to some extent upon the size and shape of the die opening. In any case, the speed is to be held down to that at which the extrusion produced is free from hot shortness. A safe extrusion speed may be ascertained by visual examination of the product as it extrudes, the hot shortness being evident as cracks in the extruded product and sharply reduced strength.

Increasing extrusion temperature and/or speed usually improves creep properties but decreases room temperature strength. Heat treatment of the extrusion at temperatures ranging from 650 to 900 F. for at least 16 hours at 650 F. and for 1 hour at 800 F. or more may also be employed to improve creep properties, particularly if the extrusion temperature and/or speed is low. We

believe that this heat treatment causes diffusion of the additive along the grain boundaries of the other constituents alloyed with the magnesium causing additional precipitation and thus improving creep properties of the composite alloy.

The additive can be in the form of either a pure metal or as a constituent of an alloy of magnesium or of another metal whose presence in magnesium is desired. Sometimes, two or more of the additives may be used together, e.g., aluminum and silicon.

The initial powdered magnesium-base alloy may consist of a mixture of various sized fine spherical particles having a fine grain structure as when produced by atomization. It is desirable to screen out and reject particles coarser than those passing through about a number 10 or 20 sieve of the standard screen scale.

If the additive is in a concentrated form, e.g., metallic silicon, the size of the particles should preferably be small, e.g., within a 0.1 to 50 micron range. The preferred size is from 1-10 microns. If the additive is a constituent of another'magnesium-base alloy, then the particle size of the alloy should be about the same as that of the initial powdered magnesium-base alloy.

The composite extrusion product may be subjected to any of the fabrication operations in use with the conventional or non-composite magnesium-base alloys, such as extrusion, rolling, forging, drawing and welding, chemical finishing, electroplating, etc., and its mechanical properties may be modified by heat treatment.

The following examples are illustrative of the invention.

Example I Fifty parts by weight of atomized magnesium-base alloy composed of 3 percent of thorium and 0.6 percent of zirconium, the balance being magnesium, passing through a number 20 sieve and being retained on a number 200 sieve, were mixed with an equal quantity of atomized magnesium-base alloy containing 1.4 percent of silicon having a particle size approximately equal to that of the aforementioned magnesium-base alloy containing thorium and zirconium. The mixture was charged into an extrusion press container as described previously. The container was heated to 650 F. The ratio of the area of the die opening to that of the container was 45. Extrusion pressure was applied, thereby compacting the charge which was extruded as the pressure was increased to about 100,000 psi. The rate of extrusion was held to about 5 feet per minute with a die temperature of 650 F. The extrusion obtained was then subjected to a conventional creep test wherein it was heated to 600 F. and a load of 3,000 psi. was applied to said extrusion. The percent creep extension Was 0.98 in 100 hours. For comparison, the same powdered magnesium-base thoriumzirconium alloy extruded alone under the same conditions of temperature, ratio of reduction in area and extrusion speed, had a percent creep extension of 3.14 in 5 minutes on applying the same conventional creep test heretofore mentioned. The additive magnesium-base silicon alloy alone had a percent creep extension after less than 1 hour which was so large that it was not readable on the relevant scale.

The extent of diffusion and precipitation which occurs in the composite product may be affected by heat treatment following the extrusion operation. As illustrative of this, the composite extrusion product of the foregoing example was heated for 1 hour at 800 F. and as a result, its percent creep extension at 600 F. and under a load of 3,000 psi. was reduced to 0.050 in hours and only 0.065 in 1000 hours.

The extent of heat treatment, that is, temperature and time, should be controlled so as to prevent excessive homogenization and thus minimize the precipitation of thorium within the grain. Excessive heat treatment, i.e., prolonged heating at high temperatures, of the composite extrusion product results in a loss of creep resistance. As illustrative of this, the composite extrusion product of the foregoing example was aged by heating for 1 hour at 1050 F. and was subsequently aged for 24 hours at 450 F. As a result, the percent creep resistance, after less than 1 hour at 600 F. and under a load of 3,000 psi. was so great that it was not readable on the relevant scale. The amount of heat treatment, i.e., temperature and time that can be applied, depends essentially on the diffusion rates of the constituents in the magnesium-base alloy from the class which includes thorium, zirconium, misch metal, didymium, calcium and the rare earth metals and is best ascertained by trial. The higher the diffusion rate, the less heat treatment (i.e., lower temperature or shorter time, or both) should be applied.

Example II In order to show the effects on the composite product of increasing the extrusion speed which also increases the temperature of the extrude, the same procedure as set forth in Example I was carried out except that the extrusion speed was increased to 30 feet per minute. As a result, the percent creep extension as measured at 600 F. under a load of 3,000 p.s.i decreased to 0.126 after 100 hours. This is to be compared to 0.98 after 100 hours as set forth in Example I.

Example III In order to show the effects on the composite product of increasing the extrusion temperature, the same procedure as set forth in Example I was carried out except that the extrusion temperature was increased to 900 F. As a result, the percent creep extension at 600 F. under a load of 3,000 psi. decreased to 0.044 after 100 hours as compared to 0.98 after 100 hours as set forth in Example I.

Example IV In order to show the effects on the composite product of decreasing the particle size of the additive metal of Ex ample I, that is, the magnesium-base alloy containing 1.4 percent of silicon, the same procedure as set forth in Example I was carried out except that the particle size of said additive was decreased from one that would just pass through a number -20 sieve to one that would just pass through a number 100 sieve. As a result, the percent creep extension at 600 F. under a load of 3,000 psi. decreased to .22 after 100 hours as compared to 0.98 after 100 hours as set forth in Example I.

Example V The same procedure as set forth in Example'I was followed except that 50 parts by weight of powdered magnesium-base alloy containing 20 percent of thorium was substituted for the powdered magnesium-base magnesiumthorium-zirconium alloy and the mixture was extruded at 700 F. at a speed of 24 feet per minute. The resulting composite product had a percent creep extension of 2.9 at 600 F. under a load of 3,000 psi. after 100 hours and a tensile strength, at room temperature, of 50,000 p.s.i. For comparison, the same powdered magnesium-base magnesium-thorium alloy extruded alone at 730 F. and at a speed of 30 feet per minute had a percent creep extension of 0.84 after 1 hour and a percent creep extension at 600 F. under a load of 3,000 p.s.i. so great after less than 5 hours that it was not readable on the relevant scale and had a tensile strength at room temperature of 46,000 p.s.i.

Example VI On substituting an equal amount of magnesium-base alloy containing 4.7 percent of misch metal and 1.8 percent of manganese for the magnesium-base magnesiumthorium-zirconium alloy of Example I and extruding the mture at 710 F. and at a speed of 27 feet per minute, the solid composite extrusion obtained had a percent creep extension of 1.34 at 400 F. under a load of 5,000 p.s.i. after 100 hours and a tensile strength at room temperature of 47,000 p.s.i. For comparison, the same powdered magnesium-base magnesium-misch metal-manganese alloy, extruded alone at 710 F. and at a speed of 30 feet per minute, had a percent creep extension at 400 F. under a load of 5,000 p.s.i. of 0.57 in 5 minutes and a percent creep extension so great after less than 15 minutes that it was not readable on the relevant scale and a tensile strength at room temperature of 44,000 p.s.i.

Example VII On substituting an equal amount of magnesium-base alloy containing 1.4 percent of calcium and 0.3 percent zirconium for the magnesium-base magnesium-thoriumzirconium alloy of Example I and extruding the mixture at 710 F. and at a speed of 20 feet per minute, the solid composite extrusion obtained had a percent creep extension at 400 F. under a load of 5,000 p.s.i. of 1.41 in 100 hours. For comparison, the same powdered magnesiumbase magnesium-calcium-zirconium alloy, extruded alone at 700 F. and at a speed of feet per minute had a percent creep extension at 400 F. under a load of 5,000 p.s.i. so great after less than 3 hours that it was not readable on the relevant scale.

Example VIII On substituting an equal amount of magnesium-base alloy containing 3 percent of didymium and 0.6 percent of zirconium for the magnesium-base magnesium-thoriumzirconium alloy of Example I and extruding the mixture at 650 F. and at a speed of 30 feet per minute, the solid composite extrusion obtained had a percent creep extension at 600 F. under a load of 3,000 p.s.i. of 0.34 in 100 hours and a tensile strength of 43,000 p.s.i. For com parison, the same powdered magnesium-base didymiumzirconium alloy, extruded alone at 720 F. and at a speed of 30 feet per minute, had a percent creep extension at 600 F. under a load of 3,000 p.s.i. so great after less than 1 hour that it was not readable on the relevant scale and a tensile strength of 35,000 p.s.i.

Example IX In order to ascertain the results of mixing and extruding the magnesium-base alloy of Example I with a concentrated silicon additive, said magnesium-base alloy of Example I was mixed and extruded with 1 part by weight of silicon particles of about -200 mesh in size, at 650- 700 F. and at a speed of 5 feet per minute. The solid composite extrusion obtained had a percent creep extension at 600 F. under a load of 3,000 p.s.i. of 4.6 in 1540 hours. After heat treating the solid composite product for 16 hours at 700 F., the product had a percent creep extension at 600 F. under a load of 3,000 p.s.i. of 0.1 in 1540 hours.

Example X In order to ascertain the results of mixing and extruding the magnesium-base alloy of Example I with concentrated additives other than silicon, said magnesiumbase alloy of Example I was mixed and extruded with 1 part by weight of antimony particles of about 200 mesh in size, at 650-700 F. and at a speed of 5 feet per minute. The solid composite extrusion obtained had a per- 6 cent creep extension at 600 F. under a load of 3,000 p.s.i. of 4.8 in hours.

Example XI On substituting 1.5 parts by weight of aluminum of -325 mesh size for the 1 part by weight of antimony of Example X, the solid extrusion obtained by extruding at 650-700 F. and at a speed of 5 feet per minute had a percent creep extension at 600 F. under a load of 3,000 p.s.i. of 1.4 in 1000 hours.

The foregoing examples are regarded as illustrative rather than limitative as considerable variations may be made in the types and proportions of the metals in the charge to be extruded and details of operation, such as the temperature, speed of extrusion and reduction in area, within the scope of the invention. In general, increasing extrusion temperature and/ or speed usually improves creep properties but decreases room temperature strength. Precipitation heat treatment of the extrusion may also be employed to improve creep properties, particularly if the extrusion temperature and/or speed is low. Decreasing particle size of the additive increases high temperature properties of the product. The silicon, antimony or aluminum additives do not affect the ranking of the elements which improve the high temperature properties of magnesium but simply make them more elfective. Calcium, for example, is still inferior to rare earths, which are inferior to thorium. It appears that a slightly higher alloy content of the element (e.g., thorium, rare earth metals, calcium, zirconium) which is responsible for the good high temperature properties of magnesium, may be desirable because of its depletion in reacting with silicon. Other elements, e.g., zirconium or manganese, which have appreciable solid solubility in magnesium and react with silicon, antimony or aluminum in magnesium to form insoluble silicides may be useful. Other elements such as zinc which do not interact with silicon or antimony may be employed in the magnesiumbase alloy or in the additive. Silicon could be added as fine metallic silicon, if desired.

What is claimed is:

1. The method of making a solid composite high strength metal body comprising a magnesium-base alloy which consists in forming a mixture of two particulated metals, one of the metals being magnesium alloyed with at least 0.05 to 6 percent by weight of at least one magnesium-soluble element selected from the group which consists of thorium, the rare earths and calcium, the other of said metals being at least one essentially magnesiuminsoluble metal selected from the group which consists of silicon and antimony, said magnesium-insoluble metal being present in an amount of from about 0.05 to about 3 weight percent of said magnesium base alloy, and die expressing the mixture at a temperature between 650 and 950 F.

2. The method according to claim 1 in which the magnesium-insoluble metal is alloyed with a magnesiumsoluble metal.

3. The method according to claim 1 wherein the solid composite body is heated at 700 to 900 F. for l to 16 hours.

4. The method of making a solid composite high strength metal body comprising a magnesium-base alloy which consists in forming a mixture of two particulated metals, one of the metals being magnesium alloyed with at least 0.05 to 6 percent by weight of thorium, the other comprising at least 0.05 to 3 percent of said magnesiumbase alloy by weight of aluminum, and die expressing the mixture at a temperature between 650 and 950 F.

5. A composite metal body comprising two particulate metals, one of the metals being magnesium alloyed with at least 0.05 to 6 percent by weight of one magnesiumsoluble element selected from the group which consists of thorium, the rare earths and calcium and the other of said metals being at least one essentially magnesium-insoluble metal selected from the group which consists of References Cited in the file of this patent silicon and antimony, said magnesium-insoluble 'metal UNITED STATES PATENTS being present in an amount of from about 0.05 to about 3 weight percent of said magnesium base alloy. 2,011,613 Brow? et a1 1935 6. A composite metal body according to claim 5 where- 5 21659 Leontls et 1953 in the magnesium-insoluble metal is alloyed with a mag- 2,685,531 Rodda 1954 nesium-soluble metal. OTHER REFERENCES 7. A composite metal body compnsmg two particulate Leonfis: Jour n all of Metals, Novembr 1951, Pages metals, one of the metals being magnesium alloyed with at least M5 9 6 Perm by weight thorium I the 13218; i r j l if lw zlf 1952 pages 287- other comprising at least 0.05 to 3 percent of said mag- 294 Published by the A IM i nesium-base alloy by weight of aluminum. 1

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,162,511 Dec. 22, 1964 George S. Foersteret a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 61, before "lanthanum" insert zirconium (Zr) column 2, line 19, before "calc inm" insert zirconium, line 29, before "Ce," insert Zr, column 6,

lineSS, strike out "zirconium or"; same column 6, after line 40, insert the following:

Example XII On substituting an equal amount of magnesiumbase alloy containing 0.5 percent zirconium for themagnesium-base magnesium-thorium-zirconium alloy of Example I and extruding the mixture at 670 F. and at a speed of 30 feet per minute, the solid composite extrusion obtained had apercent creep extension of 0.018 at 600 F. under a load of 1000 psi after 100 hours. For cbmparison, the same powdered magnesium-base alloy containing 0.5 percent zirconium, extruded alone at 670 F and at a speed of 30 feet per minute had a percent creep extension of 0.62 percent at 650 F. under a load of 1000 psi after 100 hours 1 same column 6, lines 48 and 74, after"thorium,",i.eadh occurrence insert zirconium,

Signed and sealed this 5th day of October 1965.

(SEAL) Attest:

ERNEST W. .SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 162,511 Dec. 22, 1964 George S. Foerster et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 61, before "lanthanum" insert zirconium (Zr) column 2 line 19, before "calcium" insert zirconium, line 29, before "Ce," insert Zr, column 6, Y

line 33, strike out "zirconium or"; same column 6, after line 40, insert the following:

Example XII On substituting an equal amount of magnesiumbase alloy containing 0.5 percent zirconium for the magnesium-base magnesium-thorium-zirconium alloy of Example I and extruding the mixture at 670 F. and at a speed of 30 feet per minute, the solid composite extrusion obtained had a percent creep extension of 0 018 at 600 F under a load of 1000 psi after 100 hours For comparison, the same powdered magnesium-base a1 0y containing 0.5 percent zirconium, extruded alone at 670 F and at a speed of 30 feet per minute, had a percent creep extension of 0 .62 percent at 600 F. under a load of 1000 psi after 100 hours.

same column 6, lines 48 and 74, after "1:horium,",- each occurrence, insert zirconium,

Signed and sealed this 5th day of October 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 162 ,511 Dec. 22, 1964 George S. Foerster et a1.

It is hereby certified that error appears in the above numbered patnt requiring correction and that the said Letters Patent should read as orrected below.

Column 1, line 61, before "lanthanum"- insert zirconium (Zr) column 2, line 19, before "calcium" insert zirconium, line 29, before "Ce," insert Zr, column 6,

line 33, strike out "zirconium or"; same column 6, after line 40, insert the following:

Example XII On substituting an equal amount of magnesiumbase alloy containing 0.5 percent Zirconium for themagnesium-base magnesium-thorium-zirconium alloy of Example I and extruding the mixture at 670 F. and at a speed of 30 feet per minute, the solid composite extrusion obtained had aper-cent creep extension of 0.018 at 600 F. under a load of 1000 psi after 100 hours. For comparison, the same powdered magnesium-base al 0y containing 0.5 percent zirconium, extruded alone at 670 F. and at a speed of 30 feet per minute, had a percent creep extension of 0.62 percent at 600 F. under a load of 1000 psi after 100 hours.

same column 6, lines 48 and 74, after "thorium,",' eacih occurrence, insert zirconium,

Signed and sealed this 5th day of October 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

5. A COMPOSITE METAL, BODY COMPRISING TWO PARTICULATE METALS, ONE OF THE METALS BEING MAGNESIUM ALLOYED WITH AT LEAST 0.05 TO 6 PERCENT BY WEIGHT OF ONE MAGNESIUMSOLUBLE ELEMENT SELECTED FROM THE GROUP WHICH CONSISTS OF THORIUM, THE RARE EARTHS AND CALCIUM AND THE OTHER OF SAID METALS BEING AT LEAST ONE ESSENTIALLY MAGNESIUM-INSOLUBLE METAL SELECTED FROM THE GROUP WHICH CONSISTS OF SILICON AND ANTIMONY, SAID MAGNESIUM-INSOLUBLE METAL BEING PRESENT IN AN AMOUNT OF FROM ABOUT 0.05 TO ABOUT 3 WEIGHT PERCENT OF SAID MAGNESIUM BASE ALLOY. 